The **speed**, according to its technical definition in kinematics, is a scalar quantity that indicates the rate of motion distance per time and represents the magnitude of the change in position of an object. Its units are length and time.

\[v=\dfrac{d}{t}\]

where \(v\) is speed (also called average speed), \(d\) is distance, and \(t\) is time. In other words, speed is a measure of distance traveled over a certain amount of time. Speed is often described simply as the distance traveled per unit of time. It is how fast an object is moving. Speed at some instant, or assumed constant during a very short period of time, is called instantaneous speed.

\[v_{inst}=\dfrac{ds}{dt}\]

## Speed measuring instruments

Commonly used measuring instruments are based on mechanical, electrical and optical principles of operation. They are:

- Tachometer
- Pitot tube
- Hot wire anemometer (mono and multi-component)
- Laser-Doppler Anemometer (mono and multi-component)